Electroluminescent device, manufacturing method thereof, and display apparatus

ABSTRACT

An electroluminescent device, a manufacturing method thereof, and a display apparatus are provided. The electroluminescent device includes an anode layer, a light emitting layer, a cathode layer, a hole transport layer located between the anode layer and the light emitting layer, and a electron transport layer located between the cathode layer and the light emitting layer. The electroluminescent device further includes: a first interface modification layer between the light emitting layer and one of the hole transport layer and the electron transport layer; wherein an energy level of the first interface modification layer matches an energy level of the light emitting layer and an energy level of the one of the hole transport layer and the electron transport layer.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.16/759,779 filed on Apr. 28, 2020, which is Section 371 National StageApplication of International Application No. PCT/CN2019/101356, filed onAug. 19, 2019, entitled “ELECTROLUMINESCENT DEVICE, MANUFACTURING METHODTHEREOF, AND DISPLAY APPARATUS”, which published as WO 2020/078099 A1,on Apr. 23, 2020, and claims priority to Chinese Patent Application No.201811223778.3 filed on Oct. 19, 2018 with the Chinese NationalIntellectual Property Administration, the disclosures of which areincorporated herein by reference in their entireties.

TECHNICAL FIELD

The present disclosure relates to the field of display technology, andparticularly to an electroluminescent device, a manufacturing methodthereof, and a display apparatus.

BACKGROUND

Quantum Dot Light Emitting Diodes (QLEDs) have the advantages of such ashigh brightness, low cost, and ease of mass production, such that it haspromising prospect in the application in the next generation of thedisplay apparatus. However, the energy level barrier between thecommonly used electron/hole transport layer and the light emitting layeris so high that a high turn-on voltage of the device is resulted.

SUMMARY

An embodiment of the present disclosure provides an electroluminescentdevice, including an anode layer, a light emitting layer, a cathodelayer, a hole transport layer between the anode layer and the lightemitting layer, and an electron transport layer between the cathodelayer and the light emitting layer, wherein the electroluminescentdevice further includes: a first interface modification layer betweenthe light emitting layer and one of the hole transport layer and theelectron transport layer; wherein an energy level of the first interfacemodification layer matches an energy level of the light emitting layerand an energy level of the one of the hole transport layer and theelectron transport layer.

In some embodiments, the electroluminescent device further includes: asecond interface modification layer between the light emitting layer andthe other one of the hole transport layer and the electron transportlayer; wherein an energy level of the second interface modificationlayer matches an energy level of the light emitting layer and an energylevel of the other one of the hole transport layer and the electrontransport layer.

In some embodiments, the first interface modification layer is locatedbetween the electron transport layer and the light emitting layer, andthe highest occupied molecular orbital energy level of the firstinterface modification layer is between the highest occupied molecularorbital energy level of the electron transport layer and the highestoccupied molecular orbital energy level of the light emitting layer; andthe second interface modification layer is located between the holetransport layer and the light emitting layer, and the lowest unoccupiedmolecular orbital energy level of the second interface modificationlayer is between the lowest unoccupied molecular orbital energy level ofthe hole transport layer and the lowest unoccupied molecular orbitalenergy level of the light emitting layer.

In some embodiments, the first interface modification layer includes aquantum dot film or a perovskite polycrystalline film; and the secondinterface modification layer includes a quantum dot film or a perovskitepolycrystalline film.

In some embodiments, quantum dots in the quantum dot film have a sizebetween 2 nm and 20 nm; crystalline grains in the perovskitepolycrystalline film have a size of 2 nm to 1000 nm.

In some embodiments, the quantum dot film includes at least one of thefollowing quantum dots: quantum dots composed of Group II elements andGroup VI elements; quantum dots composed of Group III elements and GroupV elements; quantum dots composed of Group I elements, Group IIIelements, and Group V elements; quantum dots composed of Group Ielements, Group III elements, and Group VI elements; or quantum dotscomposed of Group II elements, Group IV elements and Group VI elements.

In some embodiments, the first interface modification layer includesquantum dots composed of copper indium sulfur and zinc sulfide, orquantum dots composed of cadmium selenide and zinc sulfide; and thesecond interface modification layer includes quantum dots composed ofcopper indium sulfur and zinc sulfide, or quantum dots composed ofcadmium selenide and zinc sulfide.

In some embodiments, the quantum dot film includes ABX₃ type quantumdots, wherein A is an organic amine cation, B is a divalent metalcation, and X is a halogen anion.

In some embodiments, each of the first interface modification layer andthe second interface modification layer has thickness between 10 nm and1000 nm.

In some embodiments, the first interface modification layer is locatedbetween the electron transport layer and the light emitting layer, andthe lowest unoccupied molecular orbital energy level of the firstinterface modification layer is between the lowest unoccupied molecularorbital energy level of the electron transport layer and the lowestunoccupied molecular orbital energy level of the light emitting layer,wherein, the hole transport layer includes a first hole transport layerand a second hole transport layer; the first hole transport layer islocated between the second hole transport layer and the anode layer; thefirst hole transport layer is made of a mixture of a poly3,4-ethylenedioxythiophene monomer and a polystyrene sulfonate; thesecond hole transport layer is made of TFB; the first interfacemodification layer includes blue light perovskite quantum dots; theanode layer is made of indium tin oxide; the light emitting layerincludes green light perovskite quantum dots; the electron transportlayer is made of TPBi; and the cathode layer is made of Al.

In some embodiments, the hole transport layer includes a first holetransport layer and a second hole transport layer; the first holetransport layer is located between the second hole transport layer andthe anode layer; the first hole transport layer is made of a mixture ofa poly 3,4-ethylenedioxythiophene monomer and a polystyrene sulfonate;the second hole transport layer is made of TFB; the first interfacemodification layer includes quantum dots composed of cadmium selenideand zinc sulfide; the second interface modification layer includesquantum dots composed of copper indium sulfur and zinc sulfide; theanode layer is made of indium tin oxide; the light emitting layer ismade of green light perovskite film; the electron transport layer ismade of TPBi; and the cathode layer is made of Al.

In some embodiments, the electroluminescent device further includes anelectrode modification layer which is located between the electrontransport layer and the cathode layer.

In some embodiments, the electrode modification layer includes lithiumfluoride and a thickness of the electrode modification layer is between1 nm and 10 nm.

An embodiment of the present disclosure also provides a displayapparatus including the electroluminescent device as described in anyone of the above embodiments.

An embodiment of the present disclosure also provides a manufacturingmethod for an electroluminescent device, the manufacturing methodincluding: fabricating an anode layer on a base substrate; fabricating ahole transport layer on a side of the anode layer that is opposite tothe base substrate; fabricating a light emitting layer on a side of thehole transport layer that is opposite to the base substrate; fabricatingan electron transport layer on a side of the light emitting layer thatis opposite to the base substrate; and fabricating a cathode layer on aside of the electron transport layer that is opposite to the basesubstrate, wherein, the method further includes: after fabricating thehole transport layer and before fabricating the light emitting layer,forming a second interface modification layer on a side of the holetransport layer that is opposite to the base substrate, and an energylevel of the second interface modification layer matches an energy levelof the hole transport layer and an energy level of the light emittinglayer; and/or after fabricating the light emitting layer and beforefabricating the electron transport layer, forming a first interfacemodification layer on a side of the light emitting layer that isopposite to the base substrate, and an energy level of the firstinterface modification layer matches an energy level of the electrontransport layer and an energy level of the light emitting layer.

In some embodiments, the first interface modification layer includes aquantum dot film or a perovskite polycrystalline film; the secondinterface modification layer includes a quantum dot film or a perovskitepolycrystalline film.

In some embodiments, forming a second interface modification layer on aside of the hole transport layer that is opposite to the base substrateincludes: preparing a precursor solution containing an organic aminecations, divalent metal cations, and halogen anions; adding theprecursor solution into a solution containing an organic ligand,removing a top layer of solution and then centrifuging the solution toobtain perovskite quantum dots containing powders; dissolving theperovskite quantum dots containing powders in a non-polar organicsolvent, centrifuging the solvent in which the perovskite quantum dotscontaining powders are dissolved and taking supernatant to filter so asto obtain a perovskite quantum dots containing solution; andspin-coating the obtained perovskite quantum dots containing solution onthe hole transport layer; and/or wherein, forming a first interfacemodification layer on a side of the light emitting layer that isopposite to the base substrate includes: preparing a precursor solutioncontaining organic amine cations, divalent metal cations, and halogenanions; adding the precursor solution into a solution containing anorganic ligand, removing a top layer of solution and then centrifugingthe solution to obtain perovskite quantum dots containing powders;dissolving the perovskite quantum dots containing powders in a non-polarorganic solvent, centrifuging the solvent in which the perovskitequantum dots containing powders are dissolved and taking supernatant tofilter so as to obtain a perovskite quantum dots containing solution;and spin-coating the obtained perovskite quantum dots containingsolution on the light emitting layer.

In some embodiments, forming a second interface modification layer on aside of the hole transport layer that is opposite to the base substrateincludes: preparing a precursor solution containing organic aminecations, divalent metal cations, and halogen anions; and spin-coatingthe precursor solution on the hole transport layer; and/or wherein,forming a first interface modification layer on a side of the lightemitting layer that is opposite to the base substrate includes:preparing a precursor solution containing organic amine cations,divalent metal cations, and halogen anions; and spin-coating theprecursor solution on the light emitting layer.

In some embodiments, forming a second interface modification layer on aside of the hole transport layer that is opposite to the base substrateincludes: taking nanoparticles having a predetermined light-emittingpeak and then dissolving the nanoparticles in a non-polar organicsolvent to obtain a quantum dots containing solution; and filtering theobtained quantum dots containing solution and spin-coating it on thehole transport layer; and/or wherein, forming a first interfacemodification layer on a side of the light emitting layer that isopposite to the base substrate includes: taking nanoparticles having apredetermined light-emitting peak and then dissolving the nanoparticlesin a non-polar organic solvent to obtain a quantum dots containingsolution; and filtering the obtained quantum dots containing solutionand spin-coating it on the light emitting layer.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and/or additional aspects and advantages of the presentdisclosure will become apparent and easily understood from the followingdescription of the embodiments in conjunction with the accompanyingdrawings, in which:

FIG. 1 schematically shows the structure of some embodiments of theelectroluminescent device according to the present application;

FIG. 2 schematically shows the structure of the electroluminescentdevice in FIG. 1 connected to a power source;

FIG. 3 schematically shows the UV (ultraviolet) absorption spectrum andthe fluorescence emission spectrum of the blue light MAPbBr₃ quantumdots.

FIG. 4 schematically shows the energy level diagram of theelectroluminescent device in FIG. 2 ;

FIG. 5A illustrates the lines showing the current density of theelectroluminescent device as a function of voltage and the lines showingthe brightness of the electroluminescent device as a function of voltagewith and without the interface modification layer in FIG. 2 ;

FIG. 5B illustrates the lines showing the current efficiency of theelectroluminescent device as a function of the current density with andwithout the interface modification layer in FIG. 2 ;

FIG. 6 is an electroluminescence spectrum of the electroluminescentdevice in FIG. 2 under different loading voltages;

FIG. 7 schematically shows the structure of some other embodiments ofthe electroluminescent device according to the present disclosure;

FIG. 8 schematically shows the structure of the electroluminescentdevice in FIG. 1 connected to a power source;

FIG. 9 schematically shows the energy level diagram of theelectroluminescent device in FIG. 8 ;

FIG. 10A illustrates the lines showing the current density of theelectroluminescent device as a function of voltage and the lines showingthe brightness of the electroluminescent device as a function of voltagewith and without the interface modification layer in FIG. 7 ;

FIG. 10B illustrates the lines showing the current efficiency of theelectroluminescent device as a function of the current density with andwithout the interface modification layer in FIG. 7 ;

FIG. 11 schematically shows the structure of some other embodiments ofthe electroluminescent device according to the present disclosure;

FIG. 12 is a flowchart of a method for manufacturing anelectroluminescent device according to some embodiments of the presentdisclosure;

FIG. 13 is a flowchart of the method for manufacturing anelectroluminescent device according to some embodiments of the presentdisclosure; and

FIG. 14 is a flowchart of the method for manufacturing anelectroluminescent device according to still other embodiments of thepresent disclosure.

DETAILED DESCRIPTION OF EMBODIMENTS

Hereinafter, embodiments of the present disclosure will be described indetail. Examples of the embodiments are shown in the accompanyingdrawings, wherein the same or similar reference numerals represent thesame or similar elements or the elements having the same or similarfunctions throughout. The embodiments described below with reference tothe drawings are exemplary, and are only used to explain the presentdisclosure, but cannot be considered as limiting the present disclosure.

Those skilled in the art will understand that, unless specificallystated otherwise, the singular form represented by “a”, “an”, “said” and“the” may include plural form. It should be further understood that thewording “include/comprise” used in the specification of the presentdisclosure refers to the presence of the described features, integers,steps, operations, elements and/or components, but does not exclude thepresence or addition of one or more other features, integers, steps,operations, elements, components, and/or groups thereof. It isunderstood that if an element is referred to as being “connected” toanother element, it can be directly connected to the other element orintervening elements may also be present. In addition, “connection” asused herein may include wireless connection. As used herein, the term“and/or” includes all or any of the elements and all combinations of oneor more of the associated listed items.

It will be understood by those skilled in the art that, unless otherwisedefined, all terms (including technical and scientific terms) usedherein have the same meaning as commonly understood by one of ordinaryskill in the art to which this disclosure belongs. It should also beunderstood that terms such as those defined in the general dictionaryshould be understood to have meanings consistent with the meanings inthe context of the prior art, and unless specifically defined like this,they would not be explained as idealized or overly formal meaning.

In order to reduce the turn-on voltage of the device and improve itsefficiency, an embodiment of the present disclosure provides anelectroluminescent device including an anode layer, a light emittinglayer, a cathode layer, a hole transport layer between the anode layerand the light emitting layer, and an electron transport layer betweenthe cathode layer and the light emitting layer. The electroluminescentdevice further includes: a first interface modification layer located atthe electron transport layer and the light emitting layer; and/or asecond interface modification layer located between the hole transportlayer and the light emitting layer; wherein, the energy level of thesecond interface modification layer matches the energy level of the holetransport layer and the energy level of the light emitting layer; theenergy level of the first interface modification layer matches theenergy level of the electron transport layer and the energy level of thelight emitting layer.

In some embodiments of the present disclosure, a first interfacemodification layer is provided between the light emitting layer and theelectron transport layer, and/or a second interface modification layeris provided between the light emitting layer and the hole transportlayer. The energy level of the second modification layer matches theenergy level of the hole transport layer and the energy level of thelight emitting layer, and the energy level of the first interfacemodification layer matches the energy level of the electron transportlayer and the energy level of the light emitting layer, such that theelectron and/or hole injection barrier could be reduced, therebyreducing the turn-on voltage of the device and improving its efficiency.

It is understood that the first interface modification layer and thesecond interface modification layer are only intended for distinguishingthem, but do not have a special limiting effect. That is, the firstinterface modification layer may refer to the interface modificationlayer that is provided between the light emitting layer and one of thehole transport layer and the electron transport layer, while the secondinterface modification layer may refer to the interface modificationlayer that is provided between the light emitting layer and the otherone of the hole transport layer and the electron transport layer. Forconvenience of description, in the following embodiments, a descriptionis made by taking the following arrangement as example: the firstinterface modification layer is between the light emitting layer and theelectron transport layer and the second interface modification layer isbetween the light emitting layer and the hole transport layer.

Specifically, FIG. 1 schematically shows the structure of theelectroluminescent device according to some embodiments of the presentapplication. As shown in FIG. 1 , the electroluminescent device includesan anode layer 1, a light emitting layer 4, a cathode layer 6, a holetransport layer 2 between the anode layer 1 and the light emitting layer4, and an electron transport layer 5 between the cathode layer 6 and thelight emitting layer 4. The electroluminescent device further includes afirst interface modification layer 3 located between the electrontransport layer 5 and the light emitting layer 4.

In some embodiments, the first interface modification layer 3 includes aquantum dot film or a perovskite polycrystalline film. For example, thesize of the quantum dots in the quantum dot film is from 2 nm to 20 nm,and the size of the crystalline grain in the perovskite polycrystallinefilm is from 2 nm to 1000 nm.

In some embodiments, the quantum dot film includes at least one of thefollowing quantum dots: the quantum dot composed of Group II (e.g.,Group IIB) elements and Group VI (e.g., Group VIA) elements; the quantumdot composed of Group III (e.g., Group IIIA) elements and Group V (e.g.,Group VA) elements; the quantum dot composed of Group I (e.g., Group IB)elements, Group III (e.g., Group IIIA) elements, or Group V (e.g., GroupVA) elements; the quantum dot composed of Group I (e.g., Group IB)elements, Group III (e.g., Group IIIA) elements, and Group VI (e.g.,Group VIA) elements; or the quantum dot composed of Group II (e.g.,Group IIB) elements, Group IV (e.g., Group IVA) elements, and Group VI(e.g., Group VIA) elements.

In some embodiments, the quantum dot film includes ABX₃ type quantumdots, where A is an organic amine cation, B is a divalent metal cation,and X is a halogen anion.

For example, the first interface modification layer 3 includes quantumdots composed of copper indium sulfur and zinc sulfide, or quantum dotscomposed of cadmium selenide and zinc sulfide.

FIG. 2 schematically shows the structure of the electroluminescentdevice in FIG. 1 connected to a power source. The anode layer 1 and thecathode layer 6 are connected to a power source 10, which providescurrent to the electroluminescent device. The hole transport layer 2includes a first hole transport layer 21 and a second hole transportlayer 22. The first hole transport layer 21 is made of a mixture(PEDOT:PSS) of poly3,4-ethylenedioxythiophene monomer and polystyrenesulfonate. The second hole transport layer 22 is made of TFB (PolyR9,9-dioctylfluoren-2,7-diyl)-alt-(4,4′-(N-(4-butyl)phenyl)-diphenylamine).

As shown in FIG. 2 , the first interface modification layer 3 includes,for example, blue light emitting perovskite (hereinafter referred to as:blue light MAPbBr₃) quantum dots, where MA represents Methylamine FIG. 3shows the UV absorption spectrum (indicated by curve a) and thefluorescence emission spectrum (indicated by curve b) of the blueMAPbBr3 quantum dots. As shown in FIG. 3 , the peak of the blue lightMAPbBr3 quantum dot in the emission spectrum is located at 455 nm with aFWHM (full width at half maximum) of 15 nm.

As shown in FIG. 2 , the anode layer 1 includes for example indium tinoxide (ITO), the light emitting layer 4 includes for example green lightMAPbBr₃ quantum dots, the electron transport layer 5 includes forexample 1,3,5-tris (1-phenyl-1H-benzimidazol-2-yl) benzene (TPBi), andthe cathode layer 6 includes for example aluminum (Al).

The energy level matching, for example, means that the electron and/orhole injection barrier value of the interface modification layer fallswithin a reasonable range between the electron and/or hole injectionbarrier values of two layers adjacent to the interface modificationlayer. Specifically, FIG. 4 shows the energy level diagram of theelectroluminescent device of FIG. 2 , which shows the highest occupiedmolecular orbital energy level and the lowest unoccupied molecularorbital energy level of each layer. In the absence of the firstinterface modification layer 3, the electron injection barrier betweenthe light emitting layer 4 and the electron transport layer 5 (that is,the difference between the lowest unoccupied molecular orbital energylevel of the light emitting layer 4 and the lowest unoccupied molecularorbital energy level of the electron transport layer 5) (4.3 eV-2.9 eV)is 1.4 eV. However, after the first interface modification layer 3 isprovided between the light emitting layer 4 and the electron transportlayer 5, the electron injection barrier between the light emitting layer4 and the first interface modification layer 3 (that is, the differencebetween the lowest unoccupied molecular orbital energy level of thelight emitting layer 4 and the lowest unoccupied molecular orbitalenergy level of the first interface modification layer 3) (4.3 eV-3.6eV) is reduced to 0.7 eV. Therefore, by providing the first interfacemodification layer 3 according to the embodiments of the presentapplication in the electroluminescent device, the electron injectionbarrier is reduced from 1.4 eV to 0.7 eV. Therefore, the lowestunoccupied molecular orbital energy level of the first interfacemodification layer 3 should be between the lowest unoccupied molecularorbital energy level of the light emitting layer 4 and the lowestunoccupied molecular orbital energy level of the electron transportlayer 5, so as to obtain technical effects of reducing turn-on voltageand improving device efficiency.

Similarly, when the second interface modification layer 7 is providedbetween the light emitting layer 4 and the hole transport layer 2, thehighest occupied molecular orbital energy level of the second interfacemodification layer 7 should be between the highest occupied molecularorbital energy level of the light emitting layer 4 and the highestoccupied molecular orbital energy level of the hole transport layer 2,so as to also obtain the technical effects of reducing turn-on voltageand improving device efficiency.

In some embodiments, the second interface modification layer 7 and/orthe first interface modification layer 3 may be made of a single layer,or may include multiple sub-layers.

Further, as shown in FIG. 5A and FIG. 5B, the arrow pointing to theright in FIG. 5A represents the changing of lines showing the brightnessof the electroluminescent device as a function of voltage; and the arrowpointing to the left represents the changing of lines showing thecurrent density of the electroluminescent device as a function ofvoltage. It can be seen that, after the first interface modificationlayer 3 as disclosed in the embodiment of the present application isprovided, the turn-on voltage of the electroluminescent device isreduced from 3V to 2.6V. The maximum current efficiency of theelectroluminescent device in FIG. 5B increases from 18.29 cd/A to 21.01cd/A. Therefore, through the arrangement of the first interfacemodification layer 3, the turn-on voltage of the electroluminescentdevice is reduced, and the current efficiency and working efficiency arefurther improved.

FIG. 6 shows electroluminescent spectra of the electroluminescent devicein FIG. 2 under different loading voltages. The reference numeral 11indicates the electroluminescent spectrum of the electroluminescentdevice under a voltage of 3V. The reference numeral 12 indicates theelectroluminescent spectrum of the electroluminescent device under avoltage of 3.2V. The reference numeral 13 indicates theelectroluminescent spectrum of the electroluminescent device under avoltage of 3.4V. The reference numeral 14 indicates theelectroluminescent spectrum of the electroluminescent device under avoltage of 3.6V. As shown in FIG. 6 , after the interface modificationlayer including blue light MAPbBr₃ quantum dots is added, the lightemission peak of the device is located at 525 nm, and there is noparasitic light emission from the second hole transport layer 22 or thequantum dots of the first interface modification layer 3.

Like the electroluminescent device of the embodiment shown in FIG. 1 toFIG. 6 , FIG. 7 to FIG. 10B show an electroluminescent device of anotherembodiment of the present application respectively. As shown in FIG. 7 ,the electroluminescent device includes an anode layer 1, a lightemitting layer 4, a cathode layer 6, a hole transport layer 2 betweenthe anode layer 1 and the light emitting layer 4, and an electrontransport layer 5 between the cathode layer 6 and the light emittinglayer 4. The electroluminescent device further includes: a secondinterface modification layer 7 located between the hole transport layer2 and the light emitting layer 4; and a first interface modificationlayer 3 located between the electron transport layer 5 and the lightemitting layer 4. Each of the second interface modification layer 7 andthe first interface modification layer 3 includes a quantum dot film ora perovskite polycrystalline film.

Like the electroluminescent device of the foregoing embodiment of thepresent disclosure, for example, the size of the quantum dots in thequantum dot film in the second interface modification layer 7 is from 2nm to 20 nm, and the size of the crystalline grain in the perovskitepolycrystalline film is from 2 nm to 1000 nm.

In some embodiments, the quantum dot film includes at least one of thefollowing quantum dots: the quantum dot composed of Group II elementsand Group VI elements; the quantum dots composed of Group III elementsand Group V elements; the quantum dots composed of Group I elements,Group III elements, and Group V elements; the quantum dots composed ofGroup I elements, Group III elements, and Group VI elements; or thequantum dots composed of Group II elements, Group IV elements, and GroupVI elements.

In another embodiment, the quantum dot film includes ABX₃ type quantumdots, where A is an organic amine cation, B is a divalent metal cation,and X is a halogen Anion.

In some embodiments, the second interface modification layer 7 includesquantum dots composed of copper indium sulfur and zinc sulfide, orquantum dots composed of cadmium selenide and zinc sulfide. The firstinterface modification layer 3 includes quantum dots composed of copperindium sulfur and zinc sulfide, or quantum dots composed of cadmiumselenide and zinc sulfide.

In the embodiment of the present disclosure, a quantum dot composed ofcopper indium sulfur and zinc sulfide may have a core-shell structure,with the copper indium sulfur as the core of the quantum dot and thezinc sulfide as the shell of the quantum dot. They may collectively forma quantum dot. Similarly, in the embodiment of the present disclosure, aquantum dot composed of cadmium selenide and zinc sulfide may also havea core-shell structure, with the cadmium selenide as the core of thequantum dot and the zinc sulfide as the shell of the quantum dot. Theymay also collectively form a quantum dot.

In some embodiments, the second interface modification layer 7 and thefirst interface modification layer 3 are made of the same material. Thesecond interface modification layer 7 and the first interfacemodification layer 3 have the same thickness.

In some embodiments, the thicknesses of the first interface modificationlayer 3 and the second interface modification layer 7 may be in a rangeof 10 nm to 1000 nm.

FIG. 8 schematically shows the structure of the electroluminescentdevice in FIG. 7 connected to a power source. The hole transport layer 2includes a first hole transport layer 21 and a second hole transportlayer 22. The first hole transport layer 21 is made of a mixture (PEDOT:PSS) of poly3,4-ethylenedioxythiophene monomer and polystyrenesulfonate. The second hole transport layer 22 is made of TFB.

As shown in FIG. 8 , the second interface modification layer 7 includesfor example quantum dots composed of copper indium sulfur and zincsulfide. The first interface modification layer 3 includes for examplequantum dots composed of cadmium selenide and zinc sulfide. The anodelayer 1 includes for example ITO. The light emitting layer 4 includesfor example a green light perovskite film. The electron transport layer5 includes for example TPBi. The cathode layer 6 includes for exampleAl.

FIG. 9 shows an energy level diagram of the electroluminescent device ofFIG. 8 . In the absence of the first interface modification layer 3, theelectron injection barrier (4.3 eV−2.9 eV) is 1.4 eV. After the firstinterface modification layer 3 is added, the electron injection barrier(4.3 eV−4.0 eV) is 0.3 eV. Therefore, after the electroluminescentdevice is provided with the first interface modification layer 3 asdisclosed in the embodiment of this application, the electron injectionbarrier is reduced from 1.4 eV to 0.3 eV.

As shown in FIG. 9 , in the absence of second interface modificationlayer 7, the hole injection barrier (6.6 eV−5.3 eV) is 1.3 eV. After thesecond interface modification layer 7 is added, the hole injectionbarrier (6.6 eV−5.77 eV) is 0.83 eV. Therefore, after theelectroluminescent device is provided with the second interfacemodification layer 7 as disclosed in the embodiment of the presentapplication, the hole injection barrier is reduced from 1.3 eV to 0.83eV.

As shown in FIG. 10A and FIG. 10B, after the first interfacemodification layer 3 and the second interface modification layer 7 asdisclosed in the embodiment of the present application are provided, theturn-on voltage of the electroluminescent device is reduced from 3V to2.6V, and the maximum current efficiency of the electroluminescentdevice is increased from 18.47 cd/A to 25.8 cd/A. Therefore, through thearrangement of the first interface modification layer 3 and the secondinterface modification layer 7, the turn-on voltage of theelectroluminescent device is reduced, and the current efficiency andworking efficiency are further improved.

In some embodiments, the above electroluminescent device furtherincludes an electrode modification layer 33. The electrode modificationlayer 33 is located between the electron transport layer 5 and thecathode layer 6. The electrode modification layer 33 functions to reducethe electron injection barrier. For example, the electrode modificationlayer includes lithium fluoride (LiF). In some embodiments, thethickness of the electrode modification layer 33 may be between 1 nm and10 nm.

In addition, in another embodiment of the present disclosure, only thesecond interface modification layer 7 is provided, without the firstinterface modification layer 3, as shown in FIG. 11 . FIG. 11 shows asecond interface modification layer 7 provided between the lightemitting layer 4 and the second hole transport layer 22. This embodimentis similar to the above-mentioned embodiment, and its details will beomitted here. In addition, FIG. 11 shows the above-mentioned electrodemodification layer 33 located between the electron transport layer 5 andthe cathode layer 6. The electroluminescent device in the embodiment ofthe present disclosure may be a quantum dot light emitting diode, but isnot limited thereto.

Embodiments of the present disclosure also provide a display apparatusincluding the electroluminescent device according to any one of theabove embodiments.

In the embodiment of the present application, an interface modificationlayer is provided between the light emitting layer and the electrontransport layer and/or between the light emitting layer and the holetransport layer, such that the electron injection barrier and/or holeinjection barrier can be reduced, thereby reducing the turn-on voltageof the device and improving the device efficiency.

Embodiments of the present disclosure also provide a method formanufacturing an electroluminescent device. FIG. 12 shows an exemplaryflowchart of a method for manufacturing an electroluminescent deviceaccording to an embodiment of the present application. As shown in FIG.12 , the method for manufacturing an electroluminescent device includes:

S101: fabricating an anode layer on a base substrate;

S102: fabricating a hole transport layer on a side of the anode layerthat is opposite to the base substrate;

S103: fabricating a second interface modification layer on a side of thehole transport layer that is opposite to the base substrate;

S104: fabricating a light emitting layer on a side of the hole transportlayer that is opposite to the base substrate;

S105: fabricating an electron transport layer on a side of the lightemitting layer that is opposite to the base substrate; and

S106: fabricating a cathode layer on a side of the electron transportlayer that is opposite to the base substrate.

FIG. 13 shows another exemplary flowchart of a method of manufacturingan electroluminescent device according to an embodiment of the presentdisclosure. The method includes:

S201: fabricating an anode layer on a base substrate;

S202: fabricating a hole transport layer on a side of the anode layerthat is opposite to the base substrate;

S203: fabricating a light emitting layer on a side of the hole transportlayer that is opposite to the base substrate;

S204: fabricating a first interface modification layer on a side of thelight emitting layer that is opposite to the base substrate;

S205: fabricating an electron transport layer on a side of the lightemitting layer that is opposite to the base substrate; and

S206: fabricating a cathode layer on a side of the electron transportlayer that is opposite to the base substrate.

FIG. 14 shows another exemplary flowchart of a method of manufacturingan electroluminescent device according to another embodiment of thepresent disclosure. The method includes:

S301: fabricating an anode layer on a base substrate;

S302: fabricating a hole transport layer on a side of the anode layerthat is opposite to the base substrate;

S303: fabricating a second interface modification layer on a side of thehole transport layer that is opposite to the base substrate;

S304: fabricating a light emitting layer on a side of the secondinterface modification layer that is opposite to the base substrate;

S305: fabricating a first interface modification layer on a side of thelight emitting layer that is opposite to the base substrate;

S306: fabricating an electron transport layer on a side of the lightemitting layer that is opposite to the base substrate; and

S307: fabricating a cathode layer on a side of the electron transportlayer that is opposite to the base substrate.

The second interface modification layer and the first interfacemodification layer in the embodiments shown in FIG. 12 , FIG. 13 andFIG. 14 each include a quantum dot film or a perovskite polycrystallinefilm.

It should be noted that, in the embodiments of the present disclosure,the terms “perovskite polycrystalline film” and the “perovskite quantumdot film” refer to two different kinds of materials. The perovskitequantum dots have a strict limitation to size, generally referring tonanoparticles having the particle size from 1 nm to 20 nm, whilegenerally the grain size of the perovskite polycrystalline film is 2 nmto 1000 nm. The perovskite polycrystalline film generally refers to thefilm obtained by directly spin-coating the precursor, while theperovskite quantum dot film refers to the film that is formed bysynthesizing quantum dots firstly through thermal injection,ligand-assisted reprecipitation, and the like, then purifying thequantum dots and dispersing the quantum dots in a non-polar organicsolvent, and finally spin-coating the non-polar organic solvent.However, the manufacturing methods for the “perovskite polycrystallinefilm” and the “perovskite quantum dot film” are not limited to theabove-mentioned processes.

In some embodiments, before fabricating the cathode layer, themanufacturing method further includes: fabricating an electrodemodification layer on the electron transport layer.

In some embodiments, when the first interface modification layer and/orthe second interface modification layer includes ABX₃ type quantum dots,the first interface modification layer and/or the second interfacemodification layer may be fabricated by an ex-situ synthesis method. Theex-situ synthesis method refers to the process in which a certain kindof material may be prepared without the need of adding another one ormore element. Based on the above principles, the method for fabricatingthe second interface modification layer in the embodiment of the presentapplication includes:

preparing a precursor solution containing organic amine cations,divalent metal cations, and halogen anions;

adding the precursor solution into the solution containing an organicligand, removing the top layer of solution and then centrifuging it toobtain powders containing the perovskite quantum dots;

dissolving the perovskite quantum dots containing powders in a non-polarorganic solvent, centrifuging it and taking the supernatant to filter toobtain a perovskite quantum dots containing solution; and

spin-coating the obtained perovskite quantum dots containing solution onthe hole transport layer.

In specific implementation, the method for fabricating the secondinterface modification layer may include, for example:

dissolving lead bromide and methylamine bromide in dimethylformamide ata predetermined mass ratio to prepare a precursor solution;

stirring the n-hexane solution while adding dodecylamine, the precursorsolution, oleic acid, and acetonitrile, removing the top layer of thesolution and then centrifuging it to obtain the powder containing theperovskite quantum dots;

dissolving the perovskite quantum dots containing powders in n-heptane,performing ultrasonic and centrifuging treatment, and then taking thesupernatant to filter after the centrifuging to obtain a perovskitequantum dots containing solution;

spin-coating the obtained perovskite quantum dots containing solution onthe hole transport layer, and performing annealing process after thespin-coating.

Specifically, the method for fabricating the first interfacemodification layer may include, for example:

preparing a precursor solution containing organic amine cations,divalent metal cations, and halogen anions;

adding the precursor solution into the solution containing an organicligand, removing the top layer of solution and then centrifuging it toobtain the powders containing the perovskite quantum dots;

dissolving the perovskite quantum dots containing powders in a non-polarorganic solvent, centrifuging it and taking the supernatant to filter toobtain a perovskite quantum dots containing solution;

spin-coating the obtained perovskite quantum dots containing solution onthe light emitting layer.

In specific implementation, the method for fabricating the firstinterface modification layer includes:

dissolving lead bromide and methylamine bromide in dimethylformamide ata predetermined mass ratio to prepare a precursor solution;

stirring the n-hexane solution while adding dodecylamine, the precursorsolution, oleic acid, and acetonitrile, removing the top layer of thesolution and then centrifuging it to obtain the powders containing theperovskite quantum dots;

dissolving the powders containing the perovskite quantum dots inn-heptane, performing ultrasonic and centrifuging treatment, and thentaking the supernatant to filter after the centrifuging to obtain aperovskite quantum dots containing solution; and

spin-coating the obtained perovskite quantum dots containing solution onthe light emitting layer, and performing annealing process after thespin-coating.

When the first interface modification layer and/or the second interfacemodification layer is a perovskite polycrystalline film, the firstinterface modification layer and/or the second interface modificationlayer in the embodiment of the present disclosure may also be fabricatedby an in-situ synthesis method. In contrast to the ex-situ synthesismethod, the in-situ synthesis method refers to the process in whichanother one or more element is needed to be added during the preparationof a certain kind of material, so as to synthesize the kind of material.The difference between the in-situ synthesis method and the ex-situsynthesis method in the embodiments of the present application lies inwhether the quantum dots need to be synthesized in advance. In thein-situ synthesis method, the quantum dots are not needed to besynthesized in advance, while in the ex-situ synthesis method thequantum dots are needed to be synthesized in advance. Based on the aboveprinciples, the method for fabricating the second interface modificationlayer in the embodiment of the present disclosure may include, forexample:

preparing a precursor solution containing organic amine cations,divalent metal cations, and halogen anions; and

spin-coating the precursor solution on the hole transport layer.

As an example, the method for fabricating the first interfacemodification layer may include, for example:

preparing a precursor solution containing organic amine cations,divalent metal cations, and halogen anions; and

spin-coating the precursor solution on the light emitting layer.

In some embodiments, the method for fabricating the second interfacemodification layer includes:

taking the nanoparticles having a predetermined light-emitting peak andthen dissolving the nanoparticles in a non-polar organic solvent toobtain quantum dots containing solution, filtering the obtained quantumdots containing solution and spin-coating it on the hole transportlayer, wherein the predetermined light-emitting peak corresponds to thewavelength of 618 nm or 650 nm, and the non-polar organic solvent is,for example, ethanol.

In some embodiments, the solution formed by dissolving the nanoparticlesin the non-polar organic solvent is subjected to ultrasonic treatment.The quantum dots containing solution is filtered after being ultrasonictreated. The filtered solution is spin-coated on the hole transportlayer and then is subject to an annealing process.

In some embodiments, the method for fabricating the first interfacemodification layer includes:

taking the nanoparticles having a predetermined light-emitting peak andthen dissolving the nanoparticles in a non-polar organic solvent toobtain quantum dots containing solution;

filtering the obtained quantum dots containing solution and spin-coatingit on the light emitting layer, wherein the predetermined light-emittingpeak corresponds to the wavelength of 618 nm or 650 nm, and thenon-polar organic solvent is, for example, n-hexane.

In some embodiments, the solution formed by dissolving the nanoparticlesin the non-polar organic solvent is subjected to ultrasonic treatment.The quantum dots containing solution is filtered after being ultrasonictreated. The filtered solution is spin-coated on the light emittinglayer and then is subjected to an annealing process.

In some embodiments, the method for fabricating the second interfacemodification layer includes:

taking the nanoparticles having a predetermined light-emitting peak andthen dissolving the nanoparticles in n-octane; and applying ultrasonictreatment on the formed solution, wherein the predeterminedlight-emitting peak corresponds to the wavelength of 618 nm or 650 nm;and

filtering the quantum dots containing solution which has been ultrasonictreated, spin-coating the filtered solution on the hole transport layerand then performing an annealing process.

In some embodiments, the method for fabricating the first interfacemodification layer includes:

taking the nanoparticles having a predetermined light-emitting peak andthen dissolving the nanoparticles in n-octane, and applying ultrasonictreatment on the formed solution, wherein the predeterminedlight-emitting peak corresponds to the wavelength of 618 nm or 650 nm;and

filtering the quantum dots containing solution which has been ultrasonictreated, spin-coating the filtered solution on the light emitting layerand then performing an annealing process.

In some embodiments, a method for fabricating a light emitting layerincludes: dissolving lead bromide, methylamine bromide and3,3-diphenylpropylamine in dimethylformamide at a predetermined massratio, and stirring the formed solution;

filtering the stirred solution to obtain a precursor solution;

spin-coating the precursor solution on the second interface modificationlayer or the hole transport layer while adding toluene during thespin-coating process; and

performing an annealing process after the spin-coating.

The manufacturing method of the electroluminescent device having onlythe first interface modification layer in the above embodiments and theelectroluminescent device having both the first interface modificationlayer and the second interface modification layer in the aboveembodiments will be described in detail below.

Regarding the electroluminescent device having only the first interfacemodification layer:

Firstly, the preparation of the first interface modification layer isintroduced below. In this embodiment, a blue light perovskite(hereinafter referred to as: blue light MAPbBr₃) quantum dot film isused as the first interface modification layer. The specific method offabricating the blue light MAPbBr₃ quantum dot film includes thefollowing steps:

Dissolve 0.0734 grams of lead bromide (PbBr₂) and 0.0179 grams ofmethylamine bromide (MABr) in 500 microliters of dimethylformamide (DMF)to form a precursor solution. Take 10 ml of n-hexane into a flask andstir it quickly by a magnetic stirrer. Add 40 microliters ofdodecylamine and 0.5 ml of the precursor solution. Then, add 100microliters of oleic acid slowly to the mixed solution, and finally add6 ml of acetonitrile as a demulsifier to the system. After removing thetop layer of solution and centrifuging at 6000 rpm for 3 minutes, theprecipitated powders, i.e., the blue light MAPbBr₃ quantum dot powders,are obtained.

Next, the steps for fabricating the first interface modification layerare as follows: dissolving 10 mg of the above-mentioned blue lightMAPbBr₃ quantum dot powders in 2 ml of n-heptane, and performing anultrasonic treatment for 10 minutes to ensure that the blue lightMAPbBr₃ quantum dots are uniformly dispersed in the solvent;subsequently, performing centrifuging at a speed of 5000 rpm for 3minutes, and after the centrifuging is completed, filtering thesupernatant using a 0.22 micron filter head to obtain a clear quantumdots containing solution; finally, taking the above quantum dotscontaining solution with a pipette to perform a spin-coating process at2000 rpm for 60 seconds, and then performing an annealing process at 60°C. for 5 minutes.

In this embodiment, a green light MAPbBr₃ film is used as the lightemitting layer. The specific fabricating method is as follows:

dissolving 0.0734 grams of PbBr₂, 0.0179 grams of MABr and 40 mg of3,3-diphenylpropylamine (DPPA-Br) in 500 microliters of DMF, stirringthem at 60° C. for 2 hours, and then filtering by a 0.22 mm filter headto obtain the precursor solution for the subsequent use; finally, taking100 microliters of the above quantum dots containing solution with apipette to perform a spin-coating process at 4000 rpm for 60 seconds;once the speed reaches 4000 rpm, adding 250 microliters of toluene; andafter the spin-coating is completed, performing an annealing process at70° C. for 5 minutes so as to obtain a light emitting layer.

In an electroluminescent device having only the first interfacemodification layer, the anode layer is made of ITO (indium tin oxides),the cathode layer is made of Al, the hole transport layer is made ofPEDOT: PSS and TFB, the light emitting layer is made of green lightperovskite film, the electron transport layer is made of 1,3,5-tris(1-phenyl-1H-benzimidazol-2-yl) benzene (TPBi), and the electrodemodification layer is make of LiF.

The specific preparation steps of the electroluminescent deviceaccording to this embodiment are as follows:

Step 1: Pretreatment of Anode Layer Substrate:

1) Cleaning: wipe the corroded ITO conductive glass with absorbentcotton containing detergent, and then rinse it with deionized water;immerse the ITO conductive glass in detergent containing water to besubjected to the ultrasonic treatment for 15 minutes; and immerse theITO conductive glass in ionized water, acetone, and isopropanolsuccessively for 15 minutes to perform the ultrasonic treatment, witheach cleaning step performed twice; finally, immerse the cleaned ITOconductive glass in isopropanol for subsequent use.

2) Plasma treatment: dry the cleaned ITO glass with nitrogen gas andplace it face-up in the chamber of the plasma cleaning equipment, andperform the plasma treatment for 5 minutes.

Step 2: Fabrication of the Hole Transport Layer:

Spin-coat PEDOT: PSS on the treated ITO glass, and then perform anannealing process at 150° C. for 15 minutes. After the annealingprocess, spin-coat TFB (6 mg/ml in chlorobenzene), and then anneal at130° C. for 30 minutes.

Step 3: Fabrication of the light emitting layer: refer to theabove-mentioned fabrication method of the green light MAPbBr₃ film,which functions as the light emitting layer.

Step 4: Fabrication of the first interface modification layer: refer tothe fabrication method of the first interface modification layerdescribed above.

Step 5: Fabrication of the electron transport layer: deposit a layer ofTPBi of 30 nm by a high vacuum vapor deposition equipment, with adeposition rate of 1 (A/s).

Step 6: fabrication of the electrode: form a layer of LiF of 1 nm byvapor deposition on the electron transport layer at a deposition rate of0.5 Å/s; and then form a layer of Al of 100 nm by vapor deposition at adeposition rate of 5 Å/s. Finally, an electroluminescent deviceaccording to an embodiment of the present application is manufactured.

Regarding the electroluminescent device having both the first interfacemodification layer and the second interface modification layer in theabove embodiment, the specific steps of the manufacturing method are asfollows:

Step 1: Fabrication of the Interface Modification Layer.

In this embodiment, a copper indium sulfur (CuInS₂)/zinc sulfide (ZnS)quantum dot film is used as the second interface modification layer, anda cadmium selenide (CdSe)/Zinc sulfide (ZnS) quantum dot film is used asthe first interface modification layer. The specific fabricating processis as follows:

The second interface modification layer: dissolving 20 mg ofnanoparticles having a light-emitting peak at 618 nm in 10 ml ofethanol, and performing an ultrasonic treatment for 10 minutes to ensurethe uniform dispersion of quantum dots; filtering by a 0.22 μm filterhead to obtain a solution for the subsequent use; finally, taking a 150microliter of the above solution with a pipette to perform aspin-coating process at a speed of 2500 rpm for 60 seconds; and afterthe spin-coating, performing an annealing process at 100° C. for 10minutes to obtain a second interface modification layer.

The first interface modification layer: dissolving 30 mg ofnanoparticles having a light-emitting peak at 650 nm in 10 ml ofethanol, and performing an ultrasonic treatment for 15 minutes to ensurethe uniform dispersion of quantum dots; filtering it by a 0.22 μm filterhead to obtain a quantum dots containing solution for the subsequentuse; Finally, 150 microliters of the above solution are spin-coated witha pipette at a speed of 2500 rpm for 60 seconds. After the spin-coatingwas completed, annealing is performed at 100° C. for 10 minutes toprepare a first interface modification layer.

Step 2: Fabrication of the Light Emitting Layer

In this embodiment, a green light FAPbBr₃ film is used as the lightemitting layer, where FA represents formamidine. The fabricating methodis as follows:

dissolving 0.0734 grams of PbBr₂, 0.0179 grams of MABr and 40 mg ofDPPA-Br in 500 microliters of DMF, stirring at 60° C. for 2 hours, andthen filtering by a 0.22 μm filter head to obtain a precursor solutionfor the subsequent use; finally, taking 100 microliters of the abovesolution with a pipette to perform a spin-coating process at 4000 rpmfor 60 seconds; once the speed reaches 4000 rpm, adding 250 microlitersof toluene immediately; and after the spin-coating is completed,performing an annealing process at 70° C. for 5 minutes.

Step 3: Fabrication of the Electroluminescent Device.

Similar to the electroluminescent device with only the first interfacemodification layer, in this embodiment, the anode layer is made of ITO,the cathode layer is made of Al, the hole transport layer is made ofPEDOT: PSS and TFB, the light emitting layer is made of green lightperovskite film, the electron transport layer is made of 1,3,5-tris(1-phenyl-1H-benzimidazol-2-yl) benzene (TPBi), and the electrodemodification layer is made of lithium fluoride (LiF).

The specific preparation steps of fabricating the electroluminescentdevice having the first interface modification layer and the secondinterface modification layer in the above embodiment are as follows:

Step 1: Pretreatment of anode layer substrate:

1) Cleaning: wipe the corroded ITO conductive glass with absorbentcotton containing detergent, and then rinse it with deionized water;immerse the ITO conductive glass in detergent containing water to besubjected to the ultrasonic treatment for 15 minutes; and immerse theITO conductive glass in ionized water, acetone, and isopropanol insequence for 15 minutes to perform the ultrasonic treatment, with eachcleaning step performed twice; finally, immerse the cleaned ITOconductive glass in isopropanol for subsequent use.

2) Plasma treatment: dry the cleaned ITO glass with nitrogen gas andplace it face-up in the chamber of the plasma cleaning equipment, andperform the plasma treatment for 5 minutes.

Step 2: Fabrication of the Hole Transport Layer:

Spin-coat PEDOT: PSS on the treated ITO glass, and then perform anannealing process at 150° C. for 15 minutes. After the annealingprocess, spin-coat TFB (6 mg/ml in chlorobenzene), and then anneal at130° C. for 30 minutes.

Step 3: Fabrication of the second interface modification layer: refer tothe fabrication of the second interface modification layer in Step 1mentioned above.

Step 4: Fabrication of the light emitting layer: refer to thefabrication of the light emitting layer in the Step 2 mentioned above.

Step 5: Fabrication of the first interface modification layer: refer tothe fabrication of the first interface modification layer in Step 1mentioned above.

Step 6: Fabrication of the electron transport layer: deposit a layer ofTPBi of 30 nm by a high vacuum vapor deposition equipment, with adeposition rate of 1 (A/s).

Step 7: Fabrication of the electrode: form a layer of LiF of 1 nm byvapor deposition on the electron transport layer at a deposition rate of5 Å/s; and then form a layer of Al of 100 nm by vapor deposition at adeposition rate of 5 Å/s. Finally, an electroluminescent deviceaccording to the third embodiment of the present application ismanufactured.

The beneficial effects obtained by applying the embodiments of thepresent disclosure include:

In the embodiment of the present application, an interface modificationlayer is added between the light emitting layer and the electrontransport layer and/or between the light emitting layer and the holetransport layer. Since the energy level of the first interfacemodification layer matches the energy level of the hole transport layerand the energy level of the light emitting layer and the energy level ofthe second interface modification layer matches the energy level of theelectron transport layer and the energy level of the light emittinglayer, the electron and/or hole injection barrier can be reduced,thereby reducing the turn-on voltage of the device and improving thedevice efficiency.

The above description is only part of the embodiments of the presentdisclosure. It is noted that, those skilled in the art could makeimprovements and modifications, which should be considered to fallwithin the scope of the present disclosure, without departing from theprinciple in the present disclosure.

What is claimed is:
 1. An electroluminescent device, comprising an anodelayer, a light emitting layer, a cathode layer, a hole transport layerbetween the anode layer and the light emitting layer, and an electrontransport layer between the cathode layer and the light emitting layer,wherein the electroluminescent device further comprises: a firstauxiliary layer between the light emitting layer and the electrontransport layer, wherein an energy level of the first auxiliary layermatches an energy level of the light emitting layer and an energy levelof the electron transport layer; or a first auxiliary layer between thelight emitting layer and the hole transport layer, wherein an energylevel of the first auxiliary layer matches an energy level of the lightemitting layer and an energy level of the hole transport layer.
 2. Theelectroluminescent device according to claim 1, wherein the firstauxiliary layer is provided between the light emitting layer and theelectron transport layer, and the lowest unoccupied molecular orbitalenergy level of the first auxiliary layer is between the lowestunoccupied molecular orbital energy level of the electron transportlayer and the lowest unoccupied molecular orbital energy level of thelight emitting layer.
 3. The electroluminescent device according toclaim 1, wherein a material of the first auxiliary layer is differentfrom a material of the electron transport layer.
 4. Theelectroluminescent device according to claim 2, further comprising asecond auxiliary layer between the light emitting layer and the holetransport layer, wherein the highest occupied molecular orbital energylevel of the second auxiliary layer is between the highest occupiedmolecular orbital energy level of the hole transport layer and thehighest occupied molecular orbital energy level of the light emittinglayer.
 5. The electroluminescent device according to claim 1, whereinthe light emitting layer is a quantum dot light emitting layer.
 6. Theelectroluminescent device according to claim 4, wherein, the firstauxiliary layer comprises a quantum dot film or a perovskitepolycrystalline film; and the second auxiliary layer comprises a quantumdot film or a perovskite polycrystalline film.
 7. The electroluminescentdevice according to claim 6, wherein, quantum dots in the quantum dotfilm have a size between 2 nm and 20 nm; crystalline grains in theperovskite polycrystalline film have a size of 2 nm to 1000 nm.